Justification of Red List CategoryThe last individual in the wild of this species died in 1987 following catastrophic declines owing to predation by the introduced brown tree-snake. A captive population survives in a snake-proof enclosure, and it breeds well in captivity. It remains classified as Extinct in the Wild until an introduced population becomes firmly established.

Population justificationNo extant population remains in the wild.

Distribution and population

Hypotaenidia owstoni is endemic to Guam (to USA), where it was widely distributed until 1968 when, along with most other indigenous species, it started to decline (Jaffe 1994). In 1981, the population was estimated at c.2,000, in 1983 it was reckoned to number fewer than 100 and, by 1987, it was extirpated from the wild (Witteman et al. (1990). It survives in captive-breeding facilities in Guam and in 15 zoos in the USA (c.159 birds in total) (Ross et al. 2011). It was reintroduced to Guam in 1998 but a rapid population decline was observed during 2000-2002 and no rails have been detected since, either in the predator free zone (Area 50, 24 hectares) or the snake reduced open landscape (Wenninger in litt. 2007). From 1989-2007 853 captive reared rails were released on nearby Rota, Northern Mariana Islands (to USA), though this has experienced mixed success, with some populations rapidly declining to extinction, populations of 40-60 individuals in the Duge area and another of 20 birds at Apanon have persisted (Wenninger in litt. 2007). In 2011, 16 rails were released on Cocos Island, a small island off the southern tip of Guam, after rats were eradicated from the island. Evidence of breeding has been observed (F. Amidon in litt. 2012).

Ecology

This flightless species was widely distributed in most habitats on Guam, including forest, savanna, scrub, secondary grassland, fern thickets and agricultural areas (Pratt et al. 1987) (but not in freshwater wetland habitats [Taylor and van Perlo 1998]). It forages along field edges and roadsides (never far from cover) for snails, slugs, insects, geckos, vegetable matter, seeds and flowers from low grasses and shrubs, and also the introduced giant African snail Achatina fulica which became an important part of the diet (Taylor 1996). It breeds throughout the year (birds attaining sexual maturity at four months) with a peak period during the rains in July-November (Haig et al. 1993). Nests are located on dry ground in dense grass, and clutch-size is 1-4, usually 3-4 (Taylor 1996).

Threats

Its decline and extinction in the wild is the result of predation by the introduced brown tree snake Boiga irregularis (Savidge 1987). Reasons for the failure of some of the introduction attempts on Rota are not known, but predation by feral cats was responsible for the failure of the reintroduction attempts on Guam (Wenninger in litt. 2007) and so feral cat control has been included as a recommended measure in the Rota release programme (F. Amidon in litt. 2012).

Conservation actions

Conservation Actions UnderwayCaptive breeding started in 1984. Since 1987, efforts have been under way to establish a self-sustaining, experimental population on the nearby snake-free island of Rota (Haig et al. 1993). In 1999, birds bred there for the first time (K. Brock per G. Wiles in litt. 1999); birds have since been released at four sites and success has been mixed (Wenninger in litt. 2007). In late 1998, some captive-reared birds were released in northern Guam, into a small area (24 ha) protected from snakes by a barrier and trapping, and though these birds were breeding (K. Brock per G. Wiles in litt. 1999), this population is now extinct (Wenninger in litt. 2007). In 2011, 16 rails were released on Cocos Island, a small island off the southern tip of Guam, after rats were eradicated from the island. Evidence of breeding has been observed (F. Amidon in litt. 2012).

Conservation Actions ProposedContinue the captive-breeding programme. Control B. irregularis and feral cats F. catus on Guam so that more introductions can take place (K. Brock per G. Wiles in litt. 1999). Undertake large-scale feral cat control program on Rota. Continue to manage the released populations on Rota to maximise the retention of the species's genetic diversity (K. Brock per G. Wiles in litt. 1999). Implement stringent measures to prevent the spread of B. irregularis from Guam to Rota. Before considering another reintroduction to Guam, control feral cats.

Recommended citation
BirdLife International (2019) Species factsheet: Hypotaenidia owstoni. Downloaded from
http://www.birdlife.org on 22/01/2019.
Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from
http://www.birdlife.org on 22/01/2019.